This invention relates to a device for detecting a fingerprint. Also, this invention relates t, an electric apparatus and a doorkeeper apparatus with built in device for detecting a fingerprint.
Conventionally, the collation of the fingerprint has been widely used to confirm and identify a person. This is because the fingerprint of each person has immutability and uniqueness. Recently, a device for detecting a fingerprint has been realized to automatically execute fingerprint collation by using the image recognition technology by a computer.
There is the following device as the example of such fingerprint detecting device. When the fingertip is pushed against the glass face of a prism, light is irradiated to the pushed place from inside of glass. A CCD (charge coupled device) camera scans a pattern of intensity of reflected light from the prism and converts the pattern photoelectrically into electricity signals. Like this, this device is using the optical technique to measure the unevenness of the fingerprint that contacted with the glass face, by detecting a variable reflection condition.
Alternately, another device comprises a pressure-sensitive sheet and matrix electrode formed on the pressure-sensitive sheet and measures a variation of the electric resistance when the sheet is pushed by a finger. A further device includes an insulator and pair of electrodes on both sides of the insulator to measure a change of capacitance between these electrodes when a fingertip pushes one of the electrodes. Other than these devices, there is a device that has sensors each of which is arranged in a matrix shape and which is formed by field effect transistor and piezoelectric thin films attached to the channel areas of the field effect transistors. The last-mentioned device can measure electric charges that occur on the piezoelectric thin films when the sensors are pushed by a fingertip.
At any rate, all of the above-mentioned devices for detecting a fingerprint are ready for detecting a fingerprint on pushing the fingerprint input section by a fingertip. This shows that the devices can not accurately detect the fingerprint due to a variation of pressure on pressing the fingertip on the fingerprint input section. Specifically, the pressure is often insufficient or too high to detect the fingerprint. In addition, the pressure that is given to the fingerprint input section is also varied or fluctuated at every person. As the result, errors are very often to happen on the detection of the fingerprint in the conventional device. This makes it difficult to accurately execute collation.